1. Field of the Invention
The present invention relates in general to control devices for controlling automotive automatic transmissions, and more particularly to control devices of a type that includes a so-called speed change completion degree estimating system that estimates the speed change compression degree assumed by the transmission, particularly estimates, upon selection of a drive range from a non-drive range, the time (or timing) when a friction element needed for the drive range starts its actual engaging operation following completion of piston stroke thereof.
2. Description of Related Art
In an automotive automatic transmission, there are installed a plurality of friction elements, such as clutches and brakes, and a hydraulic actuating means for selectively actuating the friction elements. That is, by actuating the friction elements that are selected, a certain power transmission path is provided to establish a desired gear, and by switching the friction elements that are to be actuated, another power transmission path is provided to establish another gear while carrying out a speed change of the transmission.
The transmission is powered by an engine through a torque converter. That is, the torque inputted to the transmission is outputted therefrom while being subjected to a speed change according to a selected gear.
One of the speed change completion degree estimating systems is described in Japanese Patent First Provisional Publication 6-109130. The system is constructed to estimate, upon selection of a drive range from a non-drive range, the time (or timing) when a friction element needed for the drive range starts its actual engaging operation following completion of piston stroke thereof, by detecting a speed drop from the torque converter to the transmission. That is, before starting of the engaging operation of the friction element, the hydraulic pressure for the element is so controlled as to obtain an optimum piston stroke, and after starting of the engaging operation, the hydraulic pressure is so controlled as to obtain an optimum speed change. That is, the completion of the piston stroke, namely, the timing of starting the actual engaging operation of the friction element is estimated by the drop of rotation speed of input means of the transmission.
Japanese Patent First Provisional Publication 4-366063 describes another system that estimates completion of the piston stroke, namely, the time of starting the actual engaging operation of a friction element. In this system, when, upon selection of a drive range from a non-drive range, a speed ratio between input and output speeds of a torque converter is reduced to indicate a value corresponding a drop of an input means of the transmission, estimation is so made that the friction element has finished the piston stroke, namely, started its actual engaging operation.
In the above-mentioned known systems, the estimation for completion of the piston stroke is based on the assumption that when, under standstill of an associated motor vehicle, the rotation speed of an output shaft of the transmission is 0 (zero) and when, due to engagement of the friction element, the input and output shafts of the transmission are engaged, the rotation speed of the input shaft is 0 (zero), and even under this condition, the engine is able to keep its operation due to a slip effect of the torque converter.
Accordingly, the above-mentioned systems have the following weak points due to their constructional inherence.
That is, if, during running of a vehicle (viz., transmission output shaft speed greater than 0), the driver moves the shift lever from D-range to N-range by mistake and then noticing the mistake, he or she returns the shift lever back to D-range, there is such a possibility that the rotation speed of the turbine of the torque converter (viz., transmission input shaft speed) increases with progress of the speed change in the transmission. In this case, the estimation to completion of the piston stroke of the friction element (namely, the timing of starting the actual engaging operation of the element) is not achieved.
The above matters will be clearly understood from the following explanation which is made with the aid of FIGS. 7 to 10.
That is, as is shown in FIG. 7, when, at time xe2x80x9ct1xe2x80x9d, the driver moves the shift lever back to D-range from N-range upon noticing the miss-shifting, a command value xe2x80x9cPoxe2x80x9d of hydraulic pressure of the friction element is set to instantly increase the pressure to a relatively high level for instantly completing the piston stroke as shown. However, actually, the hydraulic pressure xe2x80x9cPcxe2x80x9d fed to the friction element is forced to increase with a certain time lug, as is indicated by a solid curve.
However, during running of the vehicle, it sometimes occurs that with starting of actual engaging operation of the friction element at time xe2x80x9ct2xe2x80x9d, the turbine rotation speed xe2x80x9cNtxe2x80x9d (viz., transmission input shaft speed) is increased as shown in FIG. 7 irrespective of the engine rotation speed xe2x80x9cNexe2x80x9d. In this case, detection of the time xe2x80x9ct2xe2x80x9d when the piston stroke of the friction element is completed (viz., the actual engaging operation starts) is not achieved by the above-mentioned known estimation system because the system is constructed to use the drop of the turbine rotation speed xe2x80x9cNtxe2x80x9d as a sign of that completion.
Thus, in reality, upon sensing such sign, it becomes necessary to set the command value xe2x80x9cPoxe2x80x9d to assume the character as shown by the alternate long and two short dashes line in order that, after the time xe2x80x9ct2xe2x80x9d, the turbine rotation speed xe2x80x9cNtxe2x80x9d is smoothly increased to the level xe2x80x9cNoxe2x80x9d of transmission output shaft speed. (In the illustrated example, explanation is based on third gear having a gear ratio of 1:1, and thus, the level is equal to the transmission output shaft speed xe2x80x9cNoxe2x80x9d). Thus, it is necessary to control the actual hydraulic pressure xe2x80x9cPcxe2x80x9d in a manner as is indicated by the alternate long and short dash line.
However, actually, due to the above-mentioned reasons, even after the time xe2x80x9ct2xe2x80x9d, the command value xe2x80x9cPoxe2x80x9d is kept high that is set for controlling the piston stroke.
Accordingly, in the above-mentioned known system, the actual hydraulic pressure xe2x80x9cPcxe2x80x9d is forced to increase rapidly toward and finally to the level of the higher command value xe2x80x9cPoxe2x80x9d, as is indicated by the solid line, so that after the time xe2x80x9ct2xe2x80x9d, the turbine rotation speed xe2x80x9cNtxe2x80x9d is rapidly increased to the transmission output shaft speed irrespective of a desired speed acceleration gradient, inducing a possibility of a marked select shock.
Furthermore, as is shown in FIG. 8, after the time xe2x80x9ct2xe2x80x9d when the actual engaging operation of the friction element starts following completion of the piston stroke effected by the actual hydraulic pressure xe2x80x9cPcxe2x80x9d that is increased to follow the command value xe2x80x9cPoxe2x80x9d of hydraulic pressure due to the shift back of the shift lever from N-range to D-range at the time xe2x80x9ct1xe2x80x9d, it becomes necessary to increase the command value xe2x80x9cPoxe2x80x9d of hydraulic pressure in such manner as is indicated by the alternate long and short dash line for the purpose of smoothly effecting the change gear. However, in the known system, for the abovementioned reasons, the timing, viz., the time xe2x80x9ct2xe2x80x9d, of starting the actual engaging operation of the friction element can not be detected because the shifting from N-range to D-range is made under running of the associated vehicle. Thus, in the known system, even after the time xe2x80x9ct2xe2x80x9d, the command value xe2x80x9cPoxe2x80x9d of hydraulic pressure for the friction element is kept at the value for controlling the piston stroke as is indicated by the solid line, and thus, the actual hydraulic pressure xe2x80x9cPcxe2x80x9d is settled to the kept value of the command value xe2x80x9cPoxe2x80x9d without increasing.
Accordingly, in reality, after the time xe2x80x9ct2xe2x80x9d, with progress of the gear changing operation, it becomes necessary to smoothly bring the turbine rotation speed xe2x80x9cNtxe2x80x9d to the transmission output shaft speed as is indicated by the alternate long and short dash line. In the illustrated example, the gear ratio is 1:1 because of taking the third gear, and thus, the turbine rotation speed xe2x80x9cNtxe2x80x9d is equal to the transmission output shaft speed. However, actually, due to the above-mentioned reasons, as is indicated by the solid line, the turbine rotation speed xe2x80x9cNtxe2x80x9d fails to reach the transmission output shaft speed (viz., xe2x80x9cNoxe2x80x9d), and thus, an actual speed change progress is stopped and thus subsequent control for the hydraulic pressure is suppressed.
In order to eliminate the weak points possessed by the above-mentioned known systems, the following measures may be thought out, which will be described with reference to flowcharts of FIGS. 9 and 10. As will become apparent hereinafter, in such measures, estimation for completion of the piston stoke is carried out in respective cases.
That is, in step S31 of the flowchart of FIG. 9, the variation direction of the turbine rotation speed xe2x80x9cNtxe2x80x9d is derived, in such a manner as is depicted in the flowchart of FIG. 10.
In FIG. 10, at step S41, a current turbine rotation speed xe2x80x9cNt1xe2x80x9d is read, and at step S42, a turbine rotation speed xe2x80x9cNt2xe2x80x9d after gear change is calculated from the following equation:
Nt2=(gear ratio set after gear change)xc3x97(transmission output shaft speed xe2x80x9cNoxe2x80x9d)xe2x80x83xe2x80x83(1) 
At step S43, judgement is carried out as to whether xe2x80x9cNt1xe2x80x9d is greater than xe2x80x9cNt2xe2x80x9d or not. If YES, the operation flow goes to step S44 where it is judged that the turbine rotation speed xe2x80x9cNtxe2x80x9d has lowered. While, if NO, the operation flow goes to step S45 where it is judged that the turbine rotation speed xe2x80x9cNtxe2x80x9d has increased. The result of the step S44 or S45 goes to step S32 of the flowchart of FIG. 9.
In the flowchart of FIG. 9, if it is judged that the turbine rotation speed xe2x80x9cNtxe2x80x9d has lowered, the operation flow goes to steps S33 and S34 and judges the completion of the piston stroke (viz., starting of actual engaging operation) if the turbine rotation speed xe2x80x9cNtxe2x80x9d is lower than a predetermined level. While, if it is judged that the turbine rotation speed xe2x80x9cNtxe2x80x9d has increased, the operation flow goes to steps S35 and S36 and judges the completion of the piston stroke (viz., starting of actual engaging operation) if the turbine rotation speed xe2x80x9cNtxe2x80x9d is greater than a predetermined level.
However, the applicant notes that the above-mentioned measures are not practical because of complicated steps for estimating completion of the piston stroke.
Accordingly, an object of the present invention is to provide a speed change completion degree estimating system of an automatic transmission, which can easily estimate the speed change completion degree in every gear changes of the transmission.
Another object of the present invention is to provide a speed change control device of an automatic transmission, which controls operation of a friction element of the transmission based on information provided by the speed change completion degree estimating system.
According to a first aspect of the present invention, there is provided a speed change completion degree estimating system for use in an automatic transmission driven by an engine through a torque converter, the transmission including a plurality of friction elements which are selectively engaged to provide a selected gear thereby to transmit the power of engine to an output shaft of the transmission while changing the rotation speed. The system comprises a first section that derives a difference (Ntxe2x88x92Ne) between an input rotation speed (Nt) of the transmission and an engine rotation speed (Ne); a second section that derives a difference (gxc3x97Noxe2x88x92Ne) between the input rotation speed (gxc3x97No) of the transmission provided after completion of the speed change operation and the engine rotation speed (Ne); and a third section that calculates a speed change completion degree (Shift) of the transmission by using a ratio between the (Ntxe2x88x92Ne) and the (gxc3x97Noxe2x88x92Ne).
According to a second aspect of the present invention, there is provided a method for estimating a speed change completion degree of an automatic transmission which is driven by an engine through a torque converter, the transmission including a plurality of friction elements which are selectively engaged to provide a selected gear thereby to transmit the power of engine to an output shaft of the transmission while changing the rotation speed. The method comprises deriving a difference (Ntxe2x88x92Ne) between an input rotation speed (Nt) of the transmission and an engine rotation speed (Ne); deriving a difference (gxc3x97Noxe2x88x92Ne) between the input rotation speed (gxc3x97No) of the transmission provided after completion of the speed change operation and the engine rotation speed (Ne); and calculating a speed change completion degree (Shift) of the transmission by using a ratio between the (Ntxe2x88x92Ne) and the (gxc3x97Noxe2x88x92Ne).
According to a third aspect of the present invention, there is provided a speed change control device of an automatic transmission which is driven by an engine through a torque converter, the transmission including a plurality of friction elements which are selectively engaged to provide a selected gear thereby to transmit the power of the engine to an output shaft of the transmission while changing the rotation speed. The control device comprises a first section that derives a difference (Ntxe2x88x92Ne) between an input rotation speed (Nt) of the transmission and an engine rotation speed (Ne); a second section that derives a difference (gxc3x97Noxe2x88x92Ne) between the input rotation speed (gxc3x97No) of the transmission provided after completion of the speed change operation and the engine rotation speed (Ne); a third section that calculates a speed change completion degree (Shift) of the transmission by using a ratio between the (Ntxe2x88x92Ne) and the (gxc3x97Noxe2x88x92Ne); a fourth section that, upon shifting of a shift lever of the transmission from a non-drive range to a drive range, estimates a time when an actual engaging operation of selected one of the friction elements starts, with reference to the speed change completion degree (Shift); and a fifth section that, before the time, controls a hydraulic pressure of the selected friction element to carry out the engaging operation thereof in a first given manner and after the time, controls the hydraulic pressure to carry out the engaging operation thereof in a second given manner.
According to a fourth embodiment of the present invention, there is provided a method for controlling an automatic transmission which is driven by an engine through a torque converter, the transmission including a plurality of friction elements which are selectively engaged to provide a selected gear thereby to transmit the power of the engine to an output shaft of the transmission while changing the rotation speed. The method comprises deriving a difference (Ntxe2x88x92Ne) between an input rotation speed (Nt) of the transmission and an engine rotation speed (Ne); deriving a difference (gxc3x97Noxe2x88x92Ne) between the input rotation speed (gxc3x97No) of the transmission provided after completion of the speed change operation and the engine rotation speed (Ne); calculating a speed change completion degree (Shift) of the transmission by using a ratio between the (Ntxe2x88x92Ne) and the (gxc3x97Noxe2x88x92Ne); estimating, upon shifting of a shift lever of the transmission from a non-drive range to a drive range, a time when an actual engaging operation of selected one of the friction elements starts, with reference to the speed change completion degree (Shift); and controlling, before the time, a hydraulic pressure of the selected friction element to carry out the engaging operation thereof in a first given manner and controlling, after the time, the hydraulic pressure to carry out the engaging operation in a second given manner.